The instant invention relates to a wheel aligning tool or device for regulating the caster angle of automobile forward or rear wheels, by correcting their relationship with the chassis or sub-frame.
The natural de-regulation of the caster angle, whether positive or negative, is due to the excessive stress imparted to the forward wheels of the vehicle, whether of forward or rear traction. This condition, added to the natural metal fatigue and the poor condition of roads, makes it imperative to correct or regulate the caster angle in order to obtain a proper alignment of the vehicle wheels.
Steering features of an automobile depend on its reversibility, progression and stability conditions, which are basic for attaining comfort and safety of the driver, by providing accurate and easy driving of the vehicle.
The pivot around which the wheel rotates is not a vertical pivot, but it is forwardly directed a certain angle called a caster angle. A "wanderer" steering, an abrupt steering or a hard and dangerous steering depend on the caster angle, as well as the deviation from the road. Its wrong adjustment may also cause shimmying.
This pivot should also have a king pin inclination or outward slant measured angularly with respect to the vertical plane.
On the other hand, the stub axles should form a downward angle, called drop or camber.
Further, the front wheels are toed-in which compensates the trend of the wheels to open during running.
Shaft alignment after checking the four steering parameters, advance, outward slant, camber and convergence, is highly important since driving safety and ease, as well as life of tires will depend on their accuracy, according to manufacturing standards.
The vehicle running gear has manual means allowing controlling and correcting these parameters by an operator except angular variations which may have been produced between the fixing plate plane of the wheels and the suspension stub axles, since this is a rigid assembly, whose caster angle is factory preset.
These angular variations related to the caster angle of the wheels may be produced at the front gear as well as at the rear gear of the vehicle, with respect to the chassis or sub-frame thereof.
A caster angle regulating tool should resist the stress to which it is subjected for counterbalancing the forward part strength. This is the reason for this regulating tool. Further, such tool should be easily handled by the operator.
Basically, there are three types of tools for correcting the caster angle which differ from each other, but all of them use the coupling of the torsion lever to the wheel plate, and the support arm on the sleeve of the suspension spring, this pertaining to prior art in the public domain.
One of the known types according to Argentine Patent No. 222,604, uses a means for coupling the torsion lever to the wheel plate and a support arm at the suspension spring stub axle, assisted by two or three coupling disks for the vehicle wheel which are mounted by means of three, four or five screws to the brake drum. These disks are interchangeable for being adapted to different automobile models.
A second type of tool shown in Argentine Patent No. 222,603 uses a universal turnbuckle with lefthand screw thread and nut on one side and righthand screw thread on the opposite side, mating with a coupling disk having a plurality of holes provided to be adapted to the vehicle model involved.
A third type of tool shown in Argentine Patent No. 221,305 uses a Whitworth thread screw and nut. The position of the nut should be changed before or after the lever, depending on whether the caster angle is to be increased or decreased. This tool uses six or seven coupling disks for coupling to the wheel plate, according to the vehicle model. In an alternative embodiment, one end of the lever is provided with a pivoting bushing, allowing a better operation of the tool. The lever has a single disk with multiple holes for fixing it to different kinds of wheels.
All these arrangements have several disadvantages, one of the main disadvantages being the high force required for their operation and the short life of the mechanism, in spite of its lubrication.